02 sensor

[Krash63]

I've got a 95 k2500 7.4 litre & I believe my problem is with the 02 sensor. My question is where do the 3 wires from the sensor run? Or supposed to run to I should say...thanks

 

[grampadirt]

3 wires? My o2 has only one wire,don't know where the other 2 of yours go.

 

[PlayingWithTBI]

One wire is feedback to the PCM (it's grounded internally), the other 2 are power and ground for the heater inside the O2 sensor.

 

[Nad_Yvalhosert]

As stated, OBD1 uses a 1 wire sensor, though a heated 3 wire is a good upgrade.
Question is, what harness do you originally have? 1 wire or 3?
If you're the one upgrading, run the power wire to your fuel pump test port under the black cover, pass side firewall. The other wire should have an eyelet for a ground. At least that's how I upgraded my '95 2500 5.7's single wire that's located in the y-pipe, just upstream of the test pipe. I mean catalytic converter...

 

[Krash63]

As stated, OBD1 uses a 1 wire sensor, though a heated 3 wire is a good upgrade.
Question is, what harness do you originally have? 1 wire or 3?
If you're the one upgrading, run the power wire to your fuel pump test port under the black cover, pass side firewall. The other wire should have an eyelet for a ground. At least that's how I upgraded my '95 2500 5.7's single wire that's located in the y-pipe, just upstream of the test pipe. I mean catalytic converter...

I'm not the one doing the upgrade it was already done but it looks like it was done quickly & 1 of the wires is just hanging under the dash by the electrical connections on the driver side.a white wire

 

[Nad_Yvalhosert]

I'm not the one doing the upgrade it was already done but it looks like it was done quickly & 1 of the wires is just hanging under the dash by the electrical connections on the driver side.a white wire

If it's not wired correctly, if you're unsure if it's working correctly, and if your engine programming is stock, my suggestion is to remove the 3 wire fiasco and install the OE designed 1 wire.
There's no need to reinvent the wheel...

 

[someotherguy]

As stated, OBD1 uses a 1 wire sensor, though a heated 3 wire is a good upgrade.
Question is, what harness do you originally have? 1 wire or 3?
If you're the one upgrading, run the power wire to your fuel pump test port under the black cover, pass side firewall. The other wire should have an eyelet for a ground. At least that's how I upgraded my '95 2500 5.7's single wire that's located in the y-pipe, just upstream of the test pipe. I mean catalytic converter...

1 or 3 wire depends on year model and other equipment. Just saying OBD 1 uses the 1 wire sensor is incorrect. Many 94-95 model GMT400's use a 3 wire O2 sensor. Whether OP's does is in question; someone may have hacked his to 3 wire, or it started life as 3 wire but the wiring got damaged, as can happen. A visit to the factory service manual wiring diagram section for his specific year and equipment will tell the story plus help him determine how to repair the wiring.

Richard

 

[Nad_Yvalhosert]

Many 94-95 model GMT400's use a 3 wire O2 sensor.

Richard

In my nearly 30 years of wrenching I've never seen a factory OBD1 GMT400 with a 3 wire O2 sensor. I'll take your word that they're out there, perhaps in Commiefornia, but I've never seen one.
And I have a Cali emissions equipped '95...

 

[someotherguy]

In my nearly 30 years of wrenching I've never seen a factory OBD1 GMT400 with a 3 wire O2 sensor. I'll take your word that they're out there, perhaps in Commiefornia, but I've never seen one.
And I have a Cali emissions equipped '95...

Almost every automatic transmission 1500 and 2500LD 1994-1995 I've owned/seen/worked on are 3-wire O2. I have owned a 1994 1500 with 1 wire O2 but it was an NV4500-optioned (rare) truck, and a 1995 with 1-wire but it was a 3500HD 7.4/NV4500.

Anyway my point is a 3-wire factory O2 on a TBI era OBD 1 GMT400 isn't rare. In OP's case it may have started out as a 1 wire due to his GVWR (especially if it's a manual trans as those run the old ECM since no PCM requirement for an electronic automatic trans.)

That's why I suggested OP look in the factory service manual wiring diagrams as there's a section devoted to each specific combination one might encounter, and he'll have his answer including wire colors to watch for.

Richard

 

[Krash63]

1 or 3 wire depends on year model and other equipment. Just saying OBD 1 uses the 1 wire sensor is incorrect. Many 94-95 model GMT400's use a 3 wire O2 sensor. Whether OP's does is in question; someone may have hacked his to 3 wire, or it started life as 3 wire but the wiring got damaged, as can happen. A visit to the factory service manual wiring diagram section for his specific year and equipment will tell the story plus help him determine how to repair the wiring.

Richard

Thanks for the info Richard I'll look it up in the manual & see what it came with